A drawout is an electromechanical device to install and uninstall a molded case circuit breaker (MCCB) from a current source. For safety of the installer, a mechanical device called “autotrip plunger” must open the contacts of the MCCBs every time it is introduced or taken out from the current source. The autotrip plunger has a direct interaction with the MCCB mechanism via a tripping element, like a tripping lever, to open the contacts. The energy for doing this is provided by a compression spring called “autotrip plunger spring”.
Nowadays, market requirements for molded case circuit breakers are set to preserve the performance requirements of a molded case circuit breaker and to withstand in less frame space. For achieving this, molded case circuit breakers mechanisms are designed to have big forces compromising the internal free space for other components in the molded case circuit breaker.
There are molded case circuit breakers with a plunger which has a slot in which an internal spring can be placed. The plunger is placed between the electronic trip unit (ETU) or the thermal magnetic trip unit (TMTU) and a frame inside the molded case circuit breaker.
Other plungers of molded case circuit breakers have an internal spring in which the outer diameter of the spring is the same as the outside envelope of the plunger. The plunger is installed inside the frame of the molded case circuit breaker.